1 /*
   2  * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP
  26 #define SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP
  27 
  28 #include "gc/shared/gcCause.hpp"
  29 #include "gc/shared/gcWhen.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "runtime/handles.hpp"
  32 #include "runtime/perfData.hpp"
  33 #include "runtime/safepoint.hpp"
  34 #include "utilities/events.hpp"
  35 
  36 // A "CollectedHeap" is an implementation of a java heap for HotSpot.  This
  37 // is an abstract class: there may be many different kinds of heaps.  This
  38 // class defines the functions that a heap must implement, and contains
  39 // infrastructure common to all heaps.
  40 
  41 class AdaptiveSizePolicy;
  42 class BarrierSet;
  43 class CollectorPolicy;
  44 class GCHeapSummary;
  45 class GCTimer;
  46 class GCTracer;
  47 class MetaspaceSummary;
  48 class Thread;
  49 class ThreadClosure;
  50 class VirtualSpaceSummary;
  51 class nmethod;
  52 class WorkGang;
  53 
  54 class GCMessage : public FormatBuffer<1024> {
  55  public:
  56   bool is_before;
  57 
  58  public:
  59   GCMessage() {}
  60 };
  61 
  62 class CollectedHeap;
  63 
  64 class GCHeapLog : public EventLogBase<GCMessage> {
  65  private:
  66   void log_heap(CollectedHeap* heap, bool before);
  67 
  68  public:
  69   GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {}
  70 
  71   void log_heap_before(CollectedHeap* heap) {
  72     log_heap(heap, true);
  73   }
  74   void log_heap_after(CollectedHeap* heap) {
  75     log_heap(heap, false);
  76   }
  77 };
  78 
  79 //
  80 // CollectedHeap
  81 //   GenCollectedHeap
  82 //   G1CollectedHeap
  83 //   ShenandoahHeap
  84 //   ParallelScavengeHeap
  85 //
  86 class CollectedHeap : public CHeapObj<mtInternal> {
  87   friend class VMStructs;
  88   friend class JVMCIVMStructs;
  89   friend class IsGCActiveMark; // Block structured external access to _is_gc_active
  90 
  91  private:
  92 #ifdef ASSERT
  93   static int       _fire_out_of_memory_count;
  94 #endif
  95 
  96   GCHeapLog* _gc_heap_log;
  97 
  98   // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2
  99   // or INCLUDE_JVMCI is being used
 100   bool _defer_initial_card_mark;
 101 
 102   MemRegion _reserved;
 103 
 104  protected:
 105   BarrierSet* _barrier_set;
 106   bool _is_gc_active;
 107 
 108   // Used for filler objects (static, but initialized in ctor).
 109   static size_t _filler_array_max_size;
 110 
 111   unsigned int _total_collections;          // ... started
 112   unsigned int _total_full_collections;     // ... started
 113   NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;)
 114   NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;)
 115 
 116   // Reason for current garbage collection.  Should be set to
 117   // a value reflecting no collection between collections.
 118   GCCause::Cause _gc_cause;
 119   GCCause::Cause _gc_lastcause;
 120   PerfStringVariable* _perf_gc_cause;
 121   PerfStringVariable* _perf_gc_lastcause;
 122 
 123   // Constructor
 124   CollectedHeap();
 125 
 126   // Do common initializations that must follow instance construction,
 127   // for example, those needing virtual calls.
 128   // This code could perhaps be moved into initialize() but would
 129   // be slightly more awkward because we want the latter to be a
 130   // pure virtual.
 131   void pre_initialize();
 132 
 133   // Create a new tlab. All TLAB allocations must go through this.
 134   virtual HeapWord* allocate_new_tlab(size_t size);
 135 
 136   // Accumulate statistics on all tlabs.
 137   virtual void accumulate_statistics_all_tlabs();
 138 
 139   // Reinitialize tlabs before resuming mutators.
 140   virtual void resize_all_tlabs();
 141 
 142   // Allocate from the current thread's TLAB, with broken-out slow path.
 143   inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size);
 144   static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size);
 145 
 146   // Allocate an uninitialized block of the given size, or returns NULL if
 147   // this is impossible.
 148   inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS);
 149 
 150   // Like allocate_init, but the block returned by a successful allocation
 151   // is guaranteed initialized to zeros.
 152   inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS);
 153 
 154   // Helper functions for (VM) allocation.
 155   inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj);
 156   inline static void post_allocation_setup_no_klass_install(KlassHandle klass,
 157                                                             HeapWord* objPtr);
 158 
 159   inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size);
 160 
 161   inline static void post_allocation_setup_array(KlassHandle klass,
 162                                                  HeapWord* obj, int length);
 163 
 164   inline static void post_allocation_setup_class(KlassHandle klass, HeapWord* obj, int size);
 165 
 166   // Clears an allocated object.
 167   inline static void init_obj(HeapWord* obj, size_t size);
 168 
 169   // Filler object utilities.
 170   static inline size_t filler_array_hdr_size();
 171   static inline size_t filler_array_min_size();
 172 
 173   DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);)
 174   DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);)
 175 
 176   // Fill with a single array; caller must ensure filler_array_min_size() <=
 177   // words <= filler_array_max_size().
 178   static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true);
 179 
 180   // Fill with a single object (either an int array or a java.lang.Object).
 181   static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true);
 182 
 183   virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer);
 184 
 185   // Verification functions
 186   virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size)
 187     PRODUCT_RETURN;
 188   virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size)
 189     PRODUCT_RETURN;
 190   debug_only(static void check_for_valid_allocation_state();)
 191 
 192  public:
 193   enum Name {
 194     GenCollectedHeap,
 195     ParallelScavengeHeap,
 196     G1CollectedHeap,
 197     ShenandoahHeap
 198   };
 199 
 200   static inline size_t filler_array_max_size() {
 201     return _filler_array_max_size;
 202   }
 203 
 204   virtual Name kind() const = 0;
 205 
 206   virtual HeapWord* tlab_post_allocation_setup(HeapWord* obj);
 207 
 208   virtual const char* name() const = 0;
 209 
 210   /**
 211    * Returns JNI error code JNI_ENOMEM if memory could not be allocated,
 212    * and JNI_OK on success.
 213    */
 214   virtual jint initialize() = 0;
 215 
 216   // In many heaps, there will be a need to perform some initialization activities
 217   // after the Universe is fully formed, but before general heap allocation is allowed.
 218   // This is the correct place to place such initialization methods.
 219   virtual void post_initialize() = 0;
 220 
 221   // Stop any onging concurrent work and prepare for exit.
 222   virtual void stop() {}
 223 
 224   void initialize_reserved_region(HeapWord *start, HeapWord *end);
 225   MemRegion reserved_region() const { return _reserved; }
 226   address base() const { return (address)reserved_region().start(); }
 227 
 228   virtual size_t capacity() const = 0;
 229   virtual size_t used() const = 0;
 230 
 231   // Return "true" if the part of the heap that allocates Java
 232   // objects has reached the maximal committed limit that it can
 233   // reach, without a garbage collection.
 234   virtual bool is_maximal_no_gc() const = 0;
 235 
 236   // Support for java.lang.Runtime.maxMemory():  return the maximum amount of
 237   // memory that the vm could make available for storing 'normal' java objects.
 238   // This is based on the reserved address space, but should not include space
 239   // that the vm uses internally for bookkeeping or temporary storage
 240   // (e.g., in the case of the young gen, one of the survivor
 241   // spaces).
 242   virtual size_t max_capacity() const = 0;
 243 
 244   // Returns "TRUE" if "p" points into the reserved area of the heap.
 245   bool is_in_reserved(const void* p) const {
 246     return _reserved.contains(p);
 247   }
 248 
 249   bool is_in_reserved_or_null(const void* p) const {
 250     return p == NULL || is_in_reserved(p);
 251   }
 252 
 253   // Returns "TRUE" iff "p" points into the committed areas of the heap.
 254   // This method can be expensive so avoid using it in performance critical
 255   // code.
 256   virtual bool is_in(const void* p) const = 0;
 257 
 258   DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); })
 259 
 260   // Let's define some terms: a "closed" subset of a heap is one that
 261   //
 262   // 1) contains all currently-allocated objects, and
 263   //
 264   // 2) is closed under reference: no object in the closed subset
 265   //    references one outside the closed subset.
 266   //
 267   // Membership in a heap's closed subset is useful for assertions.
 268   // Clearly, the entire heap is a closed subset, so the default
 269   // implementation is to use "is_in_reserved".  But this may not be too
 270   // liberal to perform useful checking.  Also, the "is_in" predicate
 271   // defines a closed subset, but may be too expensive, since "is_in"
 272   // verifies that its argument points to an object head.  The
 273   // "closed_subset" method allows a heap to define an intermediate
 274   // predicate, allowing more precise checking than "is_in_reserved" at
 275   // lower cost than "is_in."
 276 
 277   // One important case is a heap composed of disjoint contiguous spaces,
 278   // such as the Garbage-First collector.  Such heaps have a convenient
 279   // closed subset consisting of the allocated portions of those
 280   // contiguous spaces.
 281 
 282   // Return "TRUE" iff the given pointer points into the heap's defined
 283   // closed subset (which defaults to the entire heap).
 284   virtual bool is_in_closed_subset(const void* p) const {
 285     return is_in_reserved(p);
 286   }
 287 
 288   bool is_in_closed_subset_or_null(const void* p) const {
 289     return p == NULL || is_in_closed_subset(p);
 290   }
 291 
 292   // An object is scavengable if its location may move during a scavenge.
 293   // (A scavenge is a GC which is not a full GC.)
 294   virtual bool is_scavengable(const void *p) = 0;
 295 
 296   void set_gc_cause(GCCause::Cause v) {
 297      if (UsePerfData) {
 298        _gc_lastcause = _gc_cause;
 299        _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
 300        _perf_gc_cause->set_value(GCCause::to_string(v));
 301      }
 302     _gc_cause = v;
 303   }
 304   GCCause::Cause gc_cause() { return _gc_cause; }
 305 
 306   // General obj/array allocation facilities.
 307   inline static oop obj_allocate(KlassHandle klass, int size, TRAPS);
 308   inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS);
 309   inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS);
 310   inline static oop class_allocate(KlassHandle klass, int size, TRAPS);
 311 
 312   virtual uint oop_extra_words();
 313 
 314 #ifndef CC_INTERP
 315   virtual void compile_prepare_oop(MacroAssembler* masm, Register obj);
 316 #endif
 317 
 318   // Raw memory allocation facilities
 319   // The obj and array allocate methods are covers for these methods.
 320   // mem_allocate() should never be
 321   // called to allocate TLABs, only individual objects.
 322   virtual HeapWord* mem_allocate(size_t size,
 323                                  bool* gc_overhead_limit_was_exceeded) = 0;
 324 
 325   // Utilities for turning raw memory into filler objects.
 326   //
 327   // min_fill_size() is the smallest region that can be filled.
 328   // fill_with_objects() can fill arbitrary-sized regions of the heap using
 329   // multiple objects.  fill_with_object() is for regions known to be smaller
 330   // than the largest array of integers; it uses a single object to fill the
 331   // region and has slightly less overhead.
 332   static size_t min_fill_size() {
 333     return size_t(align_object_size(oopDesc::header_size()));
 334   }
 335 
 336   static void fill_with_objects(HeapWord* start, size_t words, bool zap = true);
 337 
 338   static void fill_with_object(HeapWord* start, size_t words, bool zap = true);
 339   static void fill_with_object(MemRegion region, bool zap = true) {
 340     fill_with_object(region.start(), region.word_size(), zap);
 341   }
 342   static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) {
 343     fill_with_object(start, pointer_delta(end, start), zap);
 344   }
 345 
 346   // Return the address "addr" aligned by "alignment_in_bytes" if such
 347   // an address is below "end".  Return NULL otherwise.
 348   inline static HeapWord* align_allocation_or_fail(HeapWord* addr,
 349                                                    HeapWord* end,
 350                                                    unsigned short alignment_in_bytes);
 351 
 352   // Some heaps may offer a contiguous region for shared non-blocking
 353   // allocation, via inlined code (by exporting the address of the top and
 354   // end fields defining the extent of the contiguous allocation region.)
 355 
 356   // This function returns "true" iff the heap supports this kind of
 357   // allocation.  (Default is "no".)
 358   virtual bool supports_inline_contig_alloc() const {
 359     return false;
 360   }
 361   // These functions return the addresses of the fields that define the
 362   // boundaries of the contiguous allocation area.  (These fields should be
 363   // physically near to one another.)
 364   virtual HeapWord* volatile* top_addr() const {
 365     guarantee(false, "inline contiguous allocation not supported");
 366     return NULL;
 367   }
 368   virtual HeapWord** end_addr() const {
 369     guarantee(false, "inline contiguous allocation not supported");
 370     return NULL;
 371   }
 372 
 373   // Some heaps may be in an unparseable state at certain times between
 374   // collections. This may be necessary for efficient implementation of
 375   // certain allocation-related activities. Calling this function before
 376   // attempting to parse a heap ensures that the heap is in a parsable
 377   // state (provided other concurrent activity does not introduce
 378   // unparsability). It is normally expected, therefore, that this
 379   // method is invoked with the world stopped.
 380   // NOTE: if you override this method, make sure you call
 381   // super::ensure_parsability so that the non-generational
 382   // part of the work gets done. See implementation of
 383   // CollectedHeap::ensure_parsability and, for instance,
 384   // that of GenCollectedHeap::ensure_parsability().
 385   // The argument "retire_tlabs" controls whether existing TLABs
 386   // are merely filled or also retired, thus preventing further
 387   // allocation from them and necessitating allocation of new TLABs.
 388   virtual void ensure_parsability(bool retire_tlabs);
 389 
 390   // Section on thread-local allocation buffers (TLABs)
 391   // If the heap supports thread-local allocation buffers, it should override
 392   // the following methods:
 393   // Returns "true" iff the heap supports thread-local allocation buffers.
 394   // The default is "no".
 395   virtual bool supports_tlab_allocation() const = 0;
 396 
 397   // The amount of space available for thread-local allocation buffers.
 398   virtual size_t tlab_capacity(Thread *thr) const = 0;
 399 
 400   // The amount of used space for thread-local allocation buffers for the given thread.
 401   virtual size_t tlab_used(Thread *thr) const = 0;
 402 
 403   virtual size_t max_tlab_size() const;
 404 
 405   // An estimate of the maximum allocation that could be performed
 406   // for thread-local allocation buffers without triggering any
 407   // collection or expansion activity.
 408   virtual size_t unsafe_max_tlab_alloc(Thread *thr) const {
 409     guarantee(false, "thread-local allocation buffers not supported");
 410     return 0;
 411   }
 412 
 413   // Can a compiler initialize a new object without store barriers?
 414   // This permission only extends from the creation of a new object
 415   // via a TLAB up to the first subsequent safepoint. If such permission
 416   // is granted for this heap type, the compiler promises to call
 417   // defer_store_barrier() below on any slow path allocation of
 418   // a new object for which such initializing store barriers will
 419   // have been elided.
 420   virtual bool can_elide_tlab_store_barriers() const = 0;
 421 
 422   // If a compiler is eliding store barriers for TLAB-allocated objects,
 423   // there is probably a corresponding slow path which can produce
 424   // an object allocated anywhere.  The compiler's runtime support
 425   // promises to call this function on such a slow-path-allocated
 426   // object before performing initializations that have elided
 427   // store barriers. Returns new_obj, or maybe a safer copy thereof.
 428   virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj);
 429 
 430   // Answers whether an initializing store to a new object currently
 431   // allocated at the given address doesn't need a store
 432   // barrier. Returns "true" if it doesn't need an initializing
 433   // store barrier; answers "false" if it does.
 434   virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0;
 435 
 436   // If a compiler is eliding store barriers for TLAB-allocated objects,
 437   // we will be informed of a slow-path allocation by a call
 438   // to new_store_pre_barrier() above. Such a call precedes the
 439   // initialization of the object itself, and no post-store-barriers will
 440   // be issued. Some heap types require that the barrier strictly follows
 441   // the initializing stores. (This is currently implemented by deferring the
 442   // barrier until the next slow-path allocation or gc-related safepoint.)
 443   // This interface answers whether a particular heap type needs the card
 444   // mark to be thus strictly sequenced after the stores.
 445   virtual bool card_mark_must_follow_store() const = 0;
 446 
 447   // If the CollectedHeap was asked to defer a store barrier above,
 448   // this informs it to flush such a deferred store barrier to the
 449   // remembered set.
 450   virtual void flush_deferred_store_barrier(JavaThread* thread);
 451 
 452   // Perform a collection of the heap; intended for use in implementing
 453   // "System.gc".  This probably implies as full a collection as the
 454   // "CollectedHeap" supports.
 455   virtual void collect(GCCause::Cause cause) = 0;
 456 
 457   // Perform a full collection
 458   virtual void do_full_collection(bool clear_all_soft_refs) = 0;
 459 
 460   // This interface assumes that it's being called by the
 461   // vm thread. It collects the heap assuming that the
 462   // heap lock is already held and that we are executing in
 463   // the context of the vm thread.
 464   virtual void collect_as_vm_thread(GCCause::Cause cause);
 465 
 466   // Returns the barrier set for this heap
 467   BarrierSet* barrier_set() { return _barrier_set; }
 468   void set_barrier_set(BarrierSet* barrier_set);
 469 
 470   // Returns "true" iff there is a stop-world GC in progress.  (I assume
 471   // that it should answer "false" for the concurrent part of a concurrent
 472   // collector -- dld).
 473   bool is_gc_active() const { return _is_gc_active; }
 474 
 475   // Total number of GC collections (started)
 476   unsigned int total_collections() const { return _total_collections; }
 477   unsigned int total_full_collections() const { return _total_full_collections;}
 478 
 479   // Increment total number of GC collections (started)
 480   // Should be protected but used by PSMarkSweep - cleanup for 1.4.2
 481   void increment_total_collections(bool full = false) {
 482     _total_collections++;
 483     if (full) {
 484       increment_total_full_collections();
 485     }
 486   }
 487 
 488   void increment_total_full_collections() { _total_full_collections++; }
 489 
 490   // Return the AdaptiveSizePolicy for the heap.
 491   virtual AdaptiveSizePolicy* size_policy() = 0;
 492 
 493   // Return the CollectorPolicy for the heap
 494   virtual CollectorPolicy* collector_policy() const = 0;
 495 
 496   // Iterate over all objects, calling "cl.do_object" on each.
 497   virtual void object_iterate(ObjectClosure* cl) = 0;
 498 
 499   // Similar to object_iterate() except iterates only
 500   // over live objects.
 501   virtual void safe_object_iterate(ObjectClosure* cl) = 0;
 502 
 503   // NOTE! There is no requirement that a collector implement these
 504   // functions.
 505   //
 506   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,
 507   // each address in the (reserved) heap is a member of exactly
 508   // one block.  The defining characteristic of a block is that it is
 509   // possible to find its size, and thus to progress forward to the next
 510   // block.  (Blocks may be of different sizes.)  Thus, blocks may
 511   // represent Java objects, or they might be free blocks in a
 512   // free-list-based heap (or subheap), as long as the two kinds are
 513   // distinguishable and the size of each is determinable.
 514 
 515   // Returns the address of the start of the "block" that contains the
 516   // address "addr".  We say "blocks" instead of "object" since some heaps
 517   // may not pack objects densely; a chunk may either be an object or a
 518   // non-object.
 519   virtual HeapWord* block_start(const void* addr) const = 0;
 520 
 521   // Requires "addr" to be the start of a chunk, and returns its size.
 522   // "addr + size" is required to be the start of a new chunk, or the end
 523   // of the active area of the heap.
 524   virtual size_t block_size(const HeapWord* addr) const = 0;
 525 
 526   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 527   // the block is an object.
 528   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 529 
 530   // Returns the longest time (in ms) that has elapsed since the last
 531   // time that any part of the heap was examined by a garbage collection.
 532   virtual jlong millis_since_last_gc() = 0;
 533 
 534   // Perform any cleanup actions necessary before allowing a verification.
 535   virtual void prepare_for_verify() = 0;
 536 
 537   // Generate any dumps preceding or following a full gc
 538  private:
 539   void full_gc_dump(GCTimer* timer, bool before);
 540  public:
 541   void pre_full_gc_dump(GCTimer* timer);
 542   void post_full_gc_dump(GCTimer* timer);
 543 
 544   VirtualSpaceSummary create_heap_space_summary();
 545   GCHeapSummary create_heap_summary();
 546 
 547   MetaspaceSummary create_metaspace_summary();
 548 
 549   // Print heap information on the given outputStream.
 550   virtual void print_on(outputStream* st) const = 0;
 551   // The default behavior is to call print_on() on tty.
 552   virtual void print() const {
 553     print_on(tty);
 554   }
 555   // Print more detailed heap information on the given
 556   // outputStream. The default behavior is to call print_on(). It is
 557   // up to each subclass to override it and add any additional output
 558   // it needs.
 559   virtual void print_extended_on(outputStream* st) const {
 560     print_on(st);
 561   }
 562 
 563   virtual void print_on_error(outputStream* st) const;
 564 
 565   // Print all GC threads (other than the VM thread)
 566   // used by this heap.
 567   virtual void print_gc_threads_on(outputStream* st) const = 0;
 568   // The default behavior is to call print_gc_threads_on() on tty.
 569   void print_gc_threads() {
 570     print_gc_threads_on(tty);
 571   }
 572   // Iterator for all GC threads (other than VM thread)
 573   virtual void gc_threads_do(ThreadClosure* tc) const = 0;
 574 
 575   // Print any relevant tracing info that flags imply.
 576   // Default implementation does nothing.
 577   virtual void print_tracing_info() const = 0;
 578 
 579   void print_heap_before_gc();
 580   void print_heap_after_gc();
 581 
 582   // Registering and unregistering an nmethod (compiled code) with the heap.
 583   // Override with specific mechanism for each specialized heap type.
 584   virtual void register_nmethod(nmethod* nm);
 585   virtual void unregister_nmethod(nmethod* nm);
 586 
 587   // The following two methods are there to support object pinning for JNI critical
 588   // regions. They are called whenever a thread enters or leaves a JNI critical
 589   // region and requires an object not to move. Notice that there's another
 590   // mechanism for GCs to implement critical region (see gcLocker.hpp). The default
 591   // implementation does nothing.
 592   virtual void pin_object(oop o);
 593   virtual void unpin_object(oop o);
 594 
 595   void trace_heap_before_gc(const GCTracer* gc_tracer);
 596   void trace_heap_after_gc(const GCTracer* gc_tracer);
 597 
 598   // Heap verification
 599   virtual void verify(VerifyOption option) = 0;
 600 
 601   // Accumulate additional statistics from GCLABs.
 602   virtual void accumulate_statistics_all_gclabs();
 603 
 604   // Non product verification and debugging.
 605 #ifndef PRODUCT
 606   // Support for PromotionFailureALot.  Return true if it's time to cause a
 607   // promotion failure.  The no-argument version uses
 608   // this->_promotion_failure_alot_count as the counter.
 609   inline bool promotion_should_fail(volatile size_t* count);
 610   inline bool promotion_should_fail();
 611 
 612   // Reset the PromotionFailureALot counters.  Should be called at the end of a
 613   // GC in which promotion failure occurred.
 614   inline void reset_promotion_should_fail(volatile size_t* count);
 615   inline void reset_promotion_should_fail();
 616 #endif  // #ifndef PRODUCT
 617 
 618 #ifdef ASSERT
 619   static int fired_fake_oom() {
 620     return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt);
 621   }
 622 #endif
 623 
 624  public:
 625   // Copy the current allocation context statistics for the specified contexts.
 626   // For each context in contexts, set the corresponding entries in the totals
 627   // and accuracy arrays to the current values held by the statistics.  Each
 628   // array should be of length len.
 629   // Returns true if there are more stats available.
 630   virtual bool copy_allocation_context_stats(const jint* contexts,
 631                                              jlong* totals,
 632                                              jbyte* accuracy,
 633                                              jint len) {
 634     return false;
 635   }
 636 
 637 };
 638 
 639 // Class to set and reset the GC cause for a CollectedHeap.
 640 
 641 class GCCauseSetter : StackObj {
 642   CollectedHeap* _heap;
 643   GCCause::Cause _previous_cause;
 644  public:
 645   GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) {
 646     assert(SafepointSynchronize::is_at_safepoint(),
 647            "This method manipulates heap state without locking");
 648     _heap = heap;
 649     _previous_cause = _heap->gc_cause();
 650     _heap->set_gc_cause(cause);
 651   }
 652 
 653   ~GCCauseSetter() {
 654     assert(SafepointSynchronize::is_at_safepoint(),
 655           "This method manipulates heap state without locking");
 656     _heap->set_gc_cause(_previous_cause);
 657   }
 658 };
 659 
 660 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP